How is possible that i am allergic to cockroaches when i rarely see cockroaches in the first place?

It's everywhere: Cockroach is a common allergen, and lasts for years after the cockroaches are gone. It seems to me that many people become sensitized to cockroach by spending a lot of time in old schools or office buildings, which may have had a cockroach problem in the past. However, a positive skin test doesn't mean cockroach is your problem - it's a problem only if you're still exposed to the allergen.

Nocturnal critters: With cockroaches there's a big difference between seeing them rarely & never seeing them. Cockroaches are nocturnal insects that hide in the dark & come out at night. If you have seen even one cockroach in your home assume that there are many more in the walls & under cabinets & baseboards. The keys to control are meticulous cleaning, sealing every food container & a good pest control company.